Vco device

ABSTRACT

VCO (voltage-controlled oscillator) device used for a radio unit such as a television broadcast receiver. A VCO device oscillating in a wide band of oscillation frequency and capable of realizing low power consumption is provided. VCO circuit group  4  oscillates signals of frequencies corresponding to control voltage Vt applied to frequency control voltage terminal  8 . LO signal selecting means  3  selects a required output signal from VCO circuit group  4 . PLL  6  frequency-divides local signal fvco selected by LO signal selecting means  3 , compares a phase thereof with a phase of a reference signal and outputs a signal converted from a phase difference. Loop filter  7  smoothes the output signal from PLL  6 , outputs control voltage Vt that is a frequency control voltage and outputs the local-signal selected by signal selecting means  3  to high frequency signal processing means  1.

TECHNICAL FIELD

The present invention relates to a VCO (voltage-controlled oscillator )device mounted on a broadcast receiver and a communicationtransmitter/receiver, and particularly relates to a VCO deviceoscillating over a wide band of frequency.

BACKGROUND ART

A VCO device is used in, for example, a broadcast receiver and acommunication receiver and used as a circuit that generates a localfrequency for tuning any high frequency signal.

FIG. 20 is a circuit block diagram showing a conventional VCO device. InFIG. 20, VCO circuit group 104 oscillates signals of frequenciescorresponding to control voltage Vt applied to a frequency controlvoltage terminal. Current source circuit 105 sets a driving current ofan oscillation transistor (not shown) that is an element of VCO circuitgroup 104. Signal selecting means 103 selects an output signal from VCOcircuit group 104 and outputs local signal fvco to a local signal outputterminal. PLL 106 frequency-divides local signal fvco selected by signalselecting means 103, compares a phase thereof with a phase of areference signal, and outputs a voltage signal converted from a phasedifference. Loop filter 107 smoothes the output signal taken out of PLL106 and outputs control voltage Vt that controls an oscillationfrequency of local signal fvco.

In a mobile receiver including a mobile telephone, it is useful toprepare a plurality of VCO circuits 104 a, 104 b and 104 c, whichoscillate in different frequency ranges, as shown in VCO circuit group104. It is useful because such a circuit configuration is preferable inachieving downsizing of IC mounted on a mobile receiver or reduction ofpower consumption, in securing a normal operation at low power supplyvoltage and in obtaining excellent phase noise characteristics in a widefrequency range.

FIG. 21 shows a relation between frequency control voltage Vt suppliedto VCO circuits 104 a, 104 b and 104 c and the oscillation frequenciesthereof. In particular, for frequency-converting a-high frequency signalof a wide frequency range for television broadcast receiver, etc. into afirst IF signal, a VCO circuit is likewise required to oscillate a localsignal of a wide frequency range. In order to satisfy the oscillationfrequency of the local signal over a wide range, VCO circuit 104 a playsa role in oscillating in a low frequency band as an oscillationfrequency range. Furthermore, VCO circuit 104 b plays a role inoscillating in a middle frequency band as an oscillation frequencyrange, and VCO circuit 104 c plays a role in oscillating in a highfrequency as an oscillation frequency range, respectively. Thus, sinceeach of the VCO circuits plays a role respectively, a predeterminedfrequency range is oscillated, and thereby required electriccharacteristics can be obtained.

Note here that prior arts related to this kind is described in, forexample, Japanese Patent Unexamined Publication No. 9-102752.

However, when the range of oscillation frequency is intended to bewidened by using a conventional VCO device, as shown in FIG. 22, as isapparent from the relation of characteristics between the offsetfrequency and the phase noise of VCO circuits 104 a, 104 b and 104C, thesignal oscillated by VCO circuit 104 a that plays a role in oscillatingin a low frequency band of the local signal has a relatively smallerphase noise as compared with VCO circuits 104 b and 104 c.

This is because Q (Quality factor) of a resonance circuit built in theVCO circuit depends upon the frequency characteristics. As theoscillation frequency is higher, impedance of signal wiring of thecircuit or stray capacitance provided to the signal wiring becomesunignorable, and thereby Q is deteriorated. When Q of the resonancecircuit is deteriorated, the phase noise is generally increased.

As shown in FIG. 20, according to a conventional VCO device, currentsource circuit 105 for setting current of oscillation transistors (notshown) prepared for VCO circuits 104 a, 104 b and 104 c was shared bythe VCO circuits. Alternatively, when current source circuits 105 areconnected individually, the currents thereof were set to substantiallythe same value.

In such a configuration, the current of current source circuit 105 isset so that required characteristics of, for example, VCO circuit 104 c,which has the highest frequency range and is disadvantageous in loweringthe phase noise, can be achieved. Therefore, VCO circuits 104 a and 104b which are relatively advantageous in lowering the phase noisenecessarily operate below the required characteristics of the phasenoise characteristics. VCO circuits 104 a and 104 b satisfy the requiredphase noise. However, they have to supply undesired excess current,which may lead to an increase in power consumption.

When a VCO device is mounted on a mobile terminal including a mobiletelephone, continuous usable time is limited by a battery as a drivingpower supply. Therefore, it is a very important problem to achieve lowpower consumption of a broadcast receiver and a communicationtransmitter/receiver mounted on a mobile terminal.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a VCO devicecapable. of achieving both. a wide band of oscillation frequency rangeand low power consumption, and a receiver using the same.

The VCO device of the present invention includes a plurality of VCO(VOLTAGE CONTROLLED OSCILLATOR) circuits for oscillating signals offrequencies corresponding to control voltage Vt applied to a frequencycontrol voltage terminal, in different oscillation frequency ranges; acurrent source circuit for respectively setting a driving current ofeach of oscillation transistors included in the plurality of VCOcircuits; a signal selecting means for switching output signals of theVCO circuits; a PLL for frequency-dividing a local signal selected bythe signal selecting means, comparing a phase thereof with a phase of areference signal and outputting a signal converted from a phasedifference; and a loop filter for smoothing the output signal from thePLL and outputting control voltage Vt for controlling the oscillationfrequency. Thus, it is possible to achieve low power consumption inaccordance with the phase noise characteristics with respect to theoscillation frequencies of the individual VCO circuits.

Furthermore, in the VCO device of the present invention, a currentcapable of obtaining the phase noise equal to that oscillated by a VCOcircuit oscillating in the highest oscillation frequency range in theVCO circuits is applied to currents of current source circuits of otherplurality of VCO circuits. Thus, particularly, power consumption of theVCO circuit that plays a role in oscillating in a low frequency band canbe reduced.

Furthermore, in the VCO device of the present invention, current of thecurrent source circuit for driving the VCO circuit is a variable currentsource circuit. Thus, the phase noise can be corrected in accordancewith the change in a so-called operation environment such as change in atemperature or a change in power supply voltage, or switch ofcommunication specifications of different required characteristics, sothat excellent communication characteristics can be obtained.

Furthermore, the VCO device of the present invention includes aplurality of VCO circuits oscillating signals of frequenciescorresponding to control voltage Vt applied to a frequency controlvoltage terminal, and oscillating in different oscillation frequencyranges; a variable current source circuit for respectively setting adriving current of each of the plurality of VCO circuits; a highfrequency signal processing means for mixing a local signal output fromany one of the plurality of VCO circuits and a received signal inputfrom a high frequency signal input terminal; and a current control meansfor switching current of the variable current source circuitcorresponding to the oscillation frequency output from the VCO circuitgroup.

According to such a configuration, a phase noise, which changes by Q ofa resonance circuit element formed on a VCO circuit or frequencycharacteristic of parasitic capacitance, etc., can be corrected by thedriving current of the oscillation transistor. Thus, a more constantphase noise performance can be obtained over a wide band of a frequencyrange.

Furthermore, the VCO device of the present invention includes aplurality of VCO circuits for oscillating signals of frequenciescorresponding to control voltage Vt applied to a frequency controlvoltage terminal, in the different oscillation frequency ranges; andcurrent source circuits for respectively setting a driving current ofeach of the plurality of VCO circuits. In the VCO device, resonancecircuits of individual VCO circuits are set so that frequency rangesoscillating in accordance with control voltage Vt applied to a frequencycontrol voltage terminal partially overlap with each other.

Even in the case where relative variation occurs in resonance circuitsconstituting individual VCO circuits and oscillation frequency rangesset in individual VCO circuits vary in the direction of highfrequency/direction of low frequency inconsistently, the range of therequired oscillation frequency can be varied continuously into arequired oscillation frequency.

Furthermore, the VCO device of the present invention includes aplurality of VCO circuits oscillating signals of frequenciescorresponding to control voltage Vt applied to a frequency controlvoltage terminal, in different oscillation frequencies; and a currentsource circuit for respectively setting a driving current of each of theplurality of VCO circuits. In the VCO device, resonance circuits of theindividual VCO circuits are set so that the oscillation sensitivities bythe change in the oscillation frequency corresponding to control voltageVt are equalized in the individual VCO circuits. The change incapacitance of variable capacitance element is increased due to controlvoltage Vt, so that the change in the oscillation frequency isincreased. By equalizing the influence of the increase in the change ofthe oscillation frequency on the phase noise in the individual VCOcircuits, it is possible to obtain a more constant phase noiseperformance over a wide band of frequency range.

Furthermore, the VCO device of the present invention includes aplurality of VCO circuits oscillating signals of frequenciescorresponding to control voltage Vt applied to a frequency controlvoltage terminal, in different oscillation frequencies; a current sourcecircuit for respectively setting a driving current of each of theplurality of VCO circuits; a high frequency signal processing meansincluding a MIX circuit (MIX circuit is a circuit for outputting themultiplied two signals with different frequencies) connected to anoutput side of the VCO circuit and connected to an output side of thehigh frequency input signal selecting means; a signal selecting meansfor switching the output signal of the VCO circuit; a PLL forfrequency-dividing a local signal selected by the signal selectingmeans, comparing a phase thereof with a phase of a reference signal andoutputting a voltage signal converted from a phase difference; and aloop filter for smoothing the output signal from the PLL and outputtingcontrol voltage Vt for controlling the oscillation frequency.

According to such a configuration, a plurality of MIX circuits to whichthe output signal of the VCO circuit oscillating over a wide band ofoscillation frequency range is connected are provided, and signalprocessing in individual MIX circuits can be carried out in differentfrequency bands. The increase in current consumption, which has been aproblem in widening the frequency band of the MIX circuit, can beremoved. Thus, low power consumption can be achieved and excellentcommunication characteristics can be obtained.

Furthermore, the VCO device of the present invention is a VCO device inwhich a plurality of low noise amplifiers (hereinafter, which isreferred to as “LNA”) are connected to a high frequency input signalselecting means.

Thus, when each of the plurality of LNAs has a power supply ON/OFFfunction, a required high frequency input signal can be selected.Furthermore, it is possible'to obtain excellent communicationcharacteristics at low power consumption without increasing currentconsumption, which has been a problem in widening the frequency band.

Furthermore, in the VCO device of the present invention, the highfrequency input signal selecting means is configured by a plurality ofLNAs and BPFs (band pass filters).

The plurality of LNAs have power supply ON/OFF functions. Furthermore,the BPF circuit has a tuning function capable of selecting a frequency,thereby enabling the selection of high frequency input signal.Furthermore, when high frequency input signal includes interfering wavedepending upon conditions of receiving radio wave, and in particular,when the electric field strength of the interfering wave is strong, byattenuating the interfering wave by the BPF circuit, excellentcommunication characteristics can be obtained.

The VCO device of the present invention includes a plurality of VCOcircuits for oscillating signals of frequencies corresponding to controlvoltage Vt applied to a frequency control voltage terminal, in differentoscillation frequency ranges; a variable current source circuit forrespectively setting a driving current of each of the plurality of VCOcircuits; a high frequency signal processing means for mixing a localsignal output from the plurality of VCO circuits and a receiving signalinput from the high frequency signal input terminal; receivedcharacteristics judging means for judging received characteristics bycarrying out digital demodulation processing of an analog signal outputfrom the high frequency signal processing means; and current controlmeans for a switching current of the variable current source circuit byoutputting voltage or current corresponding to the digital signal outputfrom the received characteristics judging means.

Phase noise can be corrected depending upon the change in communicationcondition of a transmitting/receiving system to be mounted. Thus,excellent communication characteristics can be obtained.

The VCO device of the present invention includes a plurality of VCOcircuits for oscillating signals of frequencies corresponding to controlvoltage Vt applied to a frequency control voltage terminal, in differentoscillation frequency ranges; a variable current source circuit forrespectively setting a driving current of each of the plurality of VCOcircuits; a high frequency signal processing means for mixing a localsignal output from the plurality of VCO circuits and a received signalinput from a high frequency signal input terminal; a digital modulationsystem judging means for judging the digital modulation system bycarrying out a digital modulation processing of an analog signal outputfrom the high frequency processing means; and a current control meansfor switching current of the variable current source by outputtingvoltage or current corresponding to the digital signal output from thedigital modulation system judging means.

When broadcasting standard or communication standard to which a mountedtransmitting/receiving system corresponds uses a plurality of digitalmodulation systems, it is possible to achieve low power consumption canbe realized on the contrary to amplitude determined by these digitalmodulation systems or multiplicity on the phase axis.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit block diagram showing a VCO device of the presentinvention;

FIG. 2 is a characteristic view showing a relation between a phase noiseand a driving current of a VCO circuit of the present invention;

FIG. 3 is a circuit block diagram showing a VCO device in anotherexemplary embodiment of the present invention;

FIG. 4 is a circuit block diagram showing a VCO device in a furtherexemplary embodiment of the present invention;

FIG. 5 is a block diagram showing a VCO device using a general resonancecircuit;

FIG. 6 shows oscillation frequency ranges when variation due to an ICprocess is ignorable;

FIG. 7 shows oscillation frequency ranges when variation due to an ICprocess is not ignorable;

FIG. 8 shows oscillation frequency ranges when oscillation sensitivitiesare not constant in a plurality of VCO circuits;

FIG. 9 shows oscillation frequency ranges when oscillation sensitivitiesare constant in a plurality of VCO circuits;

FIG. 10 is a circuit block diagram showing a VCO device in a furtherexemplary embodiment of the present invention;

FIG. 11 is a circuit block diagram showing a VCO device in a furtherexemplary embodiment of the present invention;

FIG. 12 is a circuit block diagram showing a VCO device in a furtherexemplary embodiment of the present invention;

FIG. 13 is a circuit block diagram showing a VCO device in a furtherexemplary embodiment of the present invention;

FIG. 14 is a circuit block diagram showing a VCO device in a furtherexemplary embodiment of the present invention;

FIG. 15 is a correlation diagram between a phase noise and a drivingcurrent of a VCO circuit of the present invention;

FIG. 16 is a flowchart showing an example of an operation for adjustingthe current of a variable current source circuit of the presentinvention;

FIG. 17 is a circuit block diagram showing a VCO device of anotherexemplary embodiment of the present invention;

FIG. 18 is a correlation diagram between required a phase noise and thecurrent of a VCO circuit corresponding to a digital modulation system ofthe present invention; and

FIG. 19 is a flowchart showing an example of an operation of adjustingthe current in accordance with a digital modulation system in thepresent invention.

FIG. 20 is a circuit block diagram showing a conventional VCO device;

FIG. 21 is a characteristic view showing a relation between a controlvoltage and oscillation frequency in a conventional VCO device; and

FIG. 22 is a characteristic view showing an offset frequency and a phasenoise in a conventional VCO device.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, exemplary embodiments of the present invention aredescribed.

First Exemplary Embodiment

FIG. 1 is a block diagram showing an example of a VCO device of thepresent invention.

The VCO device of the present invention includes high frequency signalprocessing means 1. High frequency signal processing means 1 can beapplied to, for example, a transmitting/receiving circuit mounted on amobile terminal unit such as a mobile telephone. High frequency signalprocessing means 1 is provided with high frequency signal input terminal2 a and high frequency signal output terminal 2 b.

Furthermore, the VCO device of the present invention includes VCOcircuit group 4. VCO circuit group 4 oscillates signals of frequenciescorresponding to control voltage Vt applied to frequency control voltageterminal 8. LO signal selecting means 3 selects a required output signalfrom VCO circuit group 4. PLL 6 frequency-divides local signal fvcoselected by LO signal selecting means 3, compares a phase thereof with aphase of a reference signal, and outputs voltage signal converted from aphase difference. Loop filter 7 smoothes the output signal from PLL 6,outputs control voltage Vt for controlling the oscillation frequency oflocal signal fvco, and outputs local signal fvco selected by LO signalselecting means 3 to high frequency signal processing means 1.

Note here that a mobile terminal unit is generally required to havesmall size and low power consumption. Therefore, a VCO device mounted onthe mobile terminal unit is naturally required to have small size andlow power consumption. Furthermore, the VCO device is generally formedas an IC. Therefore, IC capable of operating normally even in a casewhere an IC package has a small size and lower power source voltage.

VCO circuit group 4 of the present invention shown in FIG. 1 ispreferable in receiving or transmitting a wide band of a frequencyrange. VCO circuit group 4 includes three VCO circuits, that is, VCOcircuit 4 a, VCO circuit 4 b and VCO circuit 4 c. Each of these threeVCO circuits is provided with a so-called oscillation transistor (notshown) for oscillating in a predetermined frequency range.

Current source circuit group 5 includes current source circuit 5 a,current source circuit 5 b and current source circuit 5 c. Currentsource circuit 5 a is provided for driving VCO circuit 4 a. Similarly,current source circuit 5 b and current source circuit 5 c are providedfor driving VCO circuit 4 b and VCO circuit 4 c, respectively. Currentsource circuits 5 a, 5 b and 5 c are set to different current valuesfrom each other. That is to say, the current source circuits 5 a, 5 band 5 c have respective roles and functions for oscillating in frequencyranges which are different from each other.

The VCO device having such a configuration of the present invention canbe operated by respectively setting a current corresponding to the phasenoise characteristics with respect to the oscillation frequency of theindividual VCO circuits oscillating in frequencies which are differentfrom each other. Thus, it is possible to set an optimum value of thephase noise of the individual VCO circuits corresponding to thefrequency characteristics or required characteristics of equipment.

FIG. 2 shows a relation between the above-mentioned phase noise andcurrent A, B and C respectively corresponding to current source circuits5 a, 5 b and 5 c.

It shows the relation between a phase noise and current values A, B andC set to three VCO circuits oscillating in different frequency ranges,that is, VCO circuit 4 a that plays a role in oscillating in a lowfrequency band, VCO circuit 4 b that plays a role in oscillating in amiddle frequency band and VCO circuit 4 c that plays a role inoscillating in a high frequency band and current source circuits 5 a, 5b and 5 c driving the three VCO circuits.

Such VCO circuits have to accept the influence of impedance or straycapacitance of the circuit. In particular, VCO circuit 4 c that plays arole in oscillating in a high frequency band is most susceptible to theinfluence. In other words, a VCO circuit that plays a role inoscillating in a low frequency band is more advantageous for achievinglow phase noise and is preferable because the current of the currentsource circuit can be reduced.

Second Exemplary Embodiment

FIG. 3 is a block diagram showing an example of another configuration ofa VCO device according to the present invention. The same orcorresponding elements shown in FIG. 1 used for describing the firstexemplary embodiment are denoted with the same reference numerals asthose therein.

The configuration of VCO circuit group 4 is the same as that in thefirst exemplary embodiment (FIG. 1). That it to say, VCO circuit group 4includes VCO circuits 4 a, 4 b and 4 c, which oscillate in differentfrequency ranges. Current source circuit group 9 is provided for drivingVCO circuit group 4. Current source circuit group 9 includes variablecurrent source circuits 8 a, 9 b and 9 c. Variable current sourcecircuit 8 ais provided for driving VCO circuit 4 a. Similarly, variablecurrent source 9 b and current source circuit 4 c are provided fordriving VCO circuit 4 b and driving 4 c, respectively.

The VCO device shown in FIG. 3 is different from that shown in FIG. 1 inthat current source circuit group 9 is a variable current source. Theother configurations, that is, the configurations of VCO circuit group4, high frequency signal processing means 1, LO signal selecting means3, PLL 6 and loop filter 7 are substantially the same as those shown inFIG. 1, and the detailed description thereof is omitted herein.

Since the VCO circuit device of the present invention shown in FIG. 3used for describing the second exemplary embodiment includes variablecurrent source circuit 9 c, a plurality of required characteristics canbe realized in accordance with not only the phase noise characteristicswith respect to the oscillation frequencies in which VCO circuits 4 a, 4b and 4 c are oscillated but also a change in the surrounding operationenvironment such as a temperature, power source voltage, or the like andcommunication standard, that is, in accordance with the surroundingenvironment, electric characteristics such as communication system,communication device, and the like.

Third Exemplary Embodiment

FIG. 4 is a block diagram showing an example of a further configurationof a VCO device of the present invention. The same or correspondingelements shown in FIG. 1 used for describing the first exemplaryembodiment and shown in FIG. 3 used for describing the second exemplaryembodiment are denoted with the same reference numerals as thosetherein, and the detailed description thereof is omitted herein.

FIG. 4 is different from the above-mentioned two exemplary embodimentsin including current control means 13 for controlling each current ofvariable current circuits 8 a, 9 b and 9 c of current source circuitgroup 9 corresponding to local signal oscillation frequency fvco andtuning means 14 for controlling the frequency in which the VCO circuitoscillates by setting a frequency-dividing ratio of PLL circuit 9.

Current control means 13 outputs voltage or current signal forcontrolling currents of current source circuit group 9 corresponding toa frequency dividing ratio setting signal output from tuning means 14.Thus, driving currents of oscillation transistor (not shown) included inVCO circuits 4 a, 4 b and 4 c can be switched.

According to the configuration of the third exemplary embodimentdescribed with reference to FIG. 4, it is possible to obtain a VCOdevice with substantially the constant phase noise even in a wide bandof frequency range.

Fourth Exemplary Embodiment

FIG. 5 is a block diagram showing a VCO device using an example of ageneral resonance circuit. In particular, it shows a specific circuitconfiguration of the VCO circuit. Furthermore, a configuration providedwith two VCO circuits oscillating in different frequency ranges isexemplified. VCO circuit 1 and VCO circuit 2 are configured by a LCparallel resonance in which a negative resistor portion (−R), aninductor L and a capacitor C are connected in parallel.

A portion where these are connected in parallel is a parallel resonancecircuit having a positive element such as a transistor supplied withpower supply voltage generating electric power. The negative resistorportion (−R) is different from general resisters in that it generateselectric power. Resonance frequency fout by LC parallel resonance can becalculated from the following equation:fout=½{√{square root over (L10·Ctotal)}}

Herein, Ctotal denotes a value of a synthesized amount of capacitance offixed capacitance capacitor C10 and C11 and variable capacitance elementCv20. Ctotal, in a case where the resonance circuit shown in FIG. 5 isconfigured, can be expressed by the following equation:${Ctotal} = {C\quad{10 \cdot \{ \frac{C\quad{11 \cdot {Cv}}\quad 20}{{C\quad 11} + {{Cv}\quad 20}} \}}}$

To change resonance frequency fout, variable capacitance element Cvwhose capacitance changes by the potential difference between bothterminals is used so as to control capacitance Cv of the variablecapacitance element by control voltage Vt output from loop filter 7,thereby enabling oscillation frequency fout to be changed.

FIGS. 6 and 7 show two oscillation frequency ranges of VCO circuit 1 andVCO circuit 2 shown in FIG. 5. FIG. 6 shows an example of an oscillationfrequency range when variation due to an IC process for producing VCOcircuits 1 and 2 is ignorable. FIG. 7 shows an example of an oscillationfrequency range when variation due to an IC process is not ignorable.

Herein, resonance frequencies fout1 and fout2 of VCO circuit 1 and VCOcircuit 2 included in the VCO device shown in FIG. 5 are calculated byusing a specific example. When control voltage Vt of variablecapacitance element Cv is set to V1=1.0V and V2=2.0V, and voltage Vt isallowed to vary in the range from V1 to V2, the range of the resonancefrequency of VCO circuit 1 and VCO circuit 2 are:

when L10=5.5 nH, C10=1.0 pF, C11=20.0 pF, L20=4.0 nH, C20=1.0 pF, C21=20pF, Cv10=Cv20=2.0 pF (Vt=V1=1.0V) and Cv10=Cv20=1.0 pF (Vt=V2=2.0V),

VCO circuit 1: 1278 MHz<fout1<1513 MHz

VCO circuit 2: 1499 MHz<fout2<1801 MHz

That is to say, in VCO circuit 1 and VCO circuit 2, corresponding tocontrol voltage Vt applied to frequency control voltage terminal 8, thefrequency ranges (1499 MHz to 1536 MHz) of the oscillation frequenciespartially overlap with each other.

Then, assuming that 4% (±2%) or 5% (±2.5%) of the relative variationoccurred in inductances (H) of inductor L10 and inductor L20 formed onthe resonance circuits of VCO circuit 1 and VCO circuit 2, and assumingthat 4% (±2%) of the relative variation occurred in the inductance infout1′ and fout2′ that is a range of the resonance frequency of VCOcircuit 1 and VCO circuit 2 under the same conditions except theinductor, and when

L10=5.61 nH=5.5 nH×1.02 (variation of +2%) and

L20=3.92 nH=5.5 nH×0.98 (variation of −2%) are satisfied,

VCO circuit 1: 1266 MHz<fout1′<1536 MHz, and

VCO circuit 2: 1522 MHz<fout2′<1829 MHz are obtained.

Furthermore, assuming that the relative variation of the inductance is5% (2.5%), and when

L10=5.64 nH=5.5 nH×1.025 (variation of +2.5%) and

L20=3.90 nH=5.5 nH×0.975 (variation of −2.5%) are satisfied,

VCO circuit 1: 1263.0 MHz<fout1′<1517.1 MHz and

VCO circuit 2: 1518.1 MHz<fout2′<1824.0 MHz are obtained.

That is to say, when the relative variation of the inductor is more than5%, a frequency range (1517.1 MHz to 1518.1 MHz) where neither VCOcircuit 1 nor VCO circuit 2 can output is turned out to appear.

In other words, since the oscillation frequency that is not continuouslyvariable occurs due to the relative variation of the inductor, in theVCO device configured by a plurality of VCO circuits, the oscillationfrequency ranges, for oscillating signals of frequencies correspondingto control voltage Vt applied to frequency control voltage terminal,partially overlap with each other.

Note here that in the fourth exemplary embodiment, the case where theinductor varies was described. However, the same is true in the casewhere an element other than the inductor such as a capacitor or avariable capacitance element varies. Therefore, by considering a complexvariation of inductor, capacitor and variable capacitance element, thecircuit constants of individual VCO circuit 1 and VCO circuit 2 aredetermined so that the oscillation frequency ranges of the plurality ofVCO circuits partially overlap with each other.

Furthermore, the fourth exemplary embodiment described the oscillationfrequency range with the relative variation of the inductor of 4% and 5%as an example. However, since the range of variation differs dependingupon IC process, it is possible to allow the oscillation frequencies ofthe plurality of VCO circuits to partially overlap with each other inaccordance with the range of variation. This is one of the designmatters of individual VCO circuits.

Furthermore, in the fourth exemplary embodiment, the case of using anunbalanced type oscillation circuit was described. Needless to say, anunbalanced type oscillation circuit using a differential amplifyingcircuit may be used.

Furthermore, in the fourth exemplary embodiment, the variablecapacitance element was used, however, any other elements may be used aslong as the element can make capacitance values variable by thepotential difference between the terminals.

Note here that FIGS. 8 and 9 show oscillation sensitivities of VCOcircuits, respectively. FIG. 8 shows a relation between the oscillationfrequency and control voltage Vt when the oscillation sensitivities arenot constant in the plurality of VCO circuits. FIG. 9 shows a relationbetween the oscillation frequency and control voltage Vt when theoscillation sensitivities are substantially constant in the plurality ofVCO circuits. FIG. 8 shows the relation between the oscillationfrequencies fout1 and fout2, which were already calculated above, andcontrol voltage Vt.

In VCO circuit 1 and VCO circuit 2 shown in FIG. 5, capacitor(C10=C20=1.0 pF, C11=C21=20.0 pF) and variable capacitance element (atVt=V1=10V, Cv10=Cv20=2.0 pF; and at Vt=V2=2.0V, Cv10=Cv20=1.0 pF) areprovided in the same configuration and by changing only the constants ofinductor 10 (=5.5 nH) and inductor 20 (=4.0 nH), different frequencyranges are obtained.

Herein, when the oscillation sensitivity of VCO circuit 1 is expressedby Δfout1/ΔVt and the oscillation sensitivity of VCO circuit 2 isexpressed by Δfout2/ΔVt,

Δfout1/ΔVt=(fout1 max-fout1 min)/(2.0-1.0)=302 MHz/V, and

Δfout2/ΔVt=(fout2 max-fout2 min)/(2.0-1.0)=258 MHz/V are obtained, whichshow that the oscillation sensitivities are different from each other.

VCO circuit 1 having larger oscillation sensitivity is more susceptibleto the influence of control voltage Vt and the phase noise is morelikely to be deteriorated. Therefore, it becomes difficult to obtain aconstant phase noise performance over a wide band of frequency range.

FIG. 9 shows a relation between the oscillation frequency and controlvoltage Vt when the oscillation sensitivities are substantially constantin the plurality of VCO circuits. The oscillation frequencies of VCOcircuit 1 and VCO circuit 2 are denoted with fout1″ and fout2″,respectively.

For adjusting the individual oscillation frequencies, the inductors (L10and L20) and capacitors (C11, C21) were used. The constant of thesevalues after modification are L10=5.3 nH, L20=4.1 nH, C11=45.0 pF andC21=9.5 pF.

Herein, similar to the above, the oscillation sensitivities aftermodification are shown. When the oscillation sensitivity of VCO circuit1 is expressed by fout1″/Δt and the oscillation sensitivity of VCOcircuit 2 is expressed by fout2″/Δ,

Δfout1″/ΔVt=(fout1″max□fout1″min)/(2.0□1.0)=274 MHz/V, and

Δfout2″/ΔVt=(fout2″max□fout2″min)/(2.0□1.0)=275 MHz/V are obtained.

As is apparent from the above description, since the oscillationsensitivities of VCO circuit 1 and VCO circuit 2 are substantially thesame, the influence of control voltage Vt on the phase noise is alsoconstant, so that more constant phase noise performance can be obtainedover a wide band of frequency range.

Note here that in the fourth exemplary embodiment, for the sake ofconvenience of description, since only one element of variablecapacitance element is used so as to control the oscillation frequencyat narrow control voltage Vt (1.0V to 2.0V), the oscillation sensitivitybecomes extremely high. However, the oscillation sensitivity ispreferably low. In particular, when a frequency range is allowed tooscillate over a wide band, the oscillation sensitivity may be loweredby using a configuration in which a plurality of elements, capable ofvarying capacitance values by the difference in potential applied to theelement between the terminals, are connected in parallel.

Fifth Exemplary Embodiment

FIG. 10 is a block diagram showing a further configuration of a VCOdevice. The same or corresponding elements shown in the first exemplaryembodiment shown in FIG. 1 are denoted with the same reference numeralsas those therein, and the detailed description thereof is omittedherein.

VCO circuit group 4 includes VCO circuits 4 a, 4 b and 4 c, whichoscillate in different oscillation frequency ranges from each other. LOsignal selecting means 3 selects one local signal from three outputsignals (local signals) of VCO circuits 4 a, 4 b and 4 c. PLL 6frequency-divides local signal fvco selected by LO signal selectingmeans 3, compares a phase thereof with a phase of a reference signal,and outputs a voltage signal converted from a phase difference.

Loop filter 7 smoothes the output signal output from PLL 6 and generatescontrol voltage Vt for controlling the oscillation frequency oscillatedby VCO circuit. Control voltage Vt output from loop filter 7 controlsthe oscillation frequency oscillated by VCO circuit 4.

Fifth exemplary embodiment shown in FIG. 10 further includes a MIXcircuit group consisting of a plurality of MIX circuits 20 a, 20 b and20 c. One input of the plurality of MIX circuits is connected to anoutput side of high frequency input signal selecting means 21.Furthermore, the other inputs of the plurality of MIX circuits areconnected to output sides of VCO circuits 4 a, 4 b and 4 c,respectively. Each of the output sides of the plurality of MIX circuits20 a, 20 b and 20 c is connected to high frequency output signalselecting means 22.

According to such a configuration, a frequency band for processingsignals by individual MIX circuits which are respectively connected tothe plurality of VCO circuits oscillating in different oscillationfrequency ranges is not a wide band such as a television broadcast but apart obtained by dividing the wide band of range. Thereby, it ispossible to obtain excellent communication characteristics at low powerconsumption without increasing the 25 current consumption, which is aproblem in widening the band of the MIX circuit.

Sixth Exemplary Embodiment

FIG. 11 is a block diagram showing an example of a further configurationof a VCO device. The same or corresponding elements shown in the fifthexemplary embodiment shown in FIG. 10 are denoted with the samereference numerals as those therein, and the detailed descriptionthereof is omitted herein.

VCO circuit group 4 includes VCO circuits 4 a, 4 b and 4 c, which areconfigured to oscillate in different oscillation frequency ranges.Furthermore, current source circuit 9 is provided. Current sourcecircuit 9 includes variable current source circuits 8 a, 9 b and 9 c.Variable current source 8 ais a diving current source of VCO circuit 4a. Similarly, variable current source 9 b and variable current source 9c are provided for driving VCO circuit 4 b and VCO circuit 4 c,respectively.

When currents of variable current source circuits 8 a, 9 b and 9 c areadjusted respectively so as to operate VCO circuits 4 a, 4 b and 4 c, itis possible to obtain a VCO device having not only phase noisecharacteristics with respect to the oscillation frequency but also aplurality of required characteristics that are different depending uponthe change in operation environment such as a temperature and powersupply voltage, etc. and communication standards.

Seventh Exemplary Embodiment

FIG. 12 is a block diagram showing an example of a further configurationof a VCO device. The same or corresponding elements shown in the sixthexemplary embodiment shown in FIG. 11 are denoted with the samereference numerals as those therein, and the detailed descriptionthereof is omitted herein.

To high frequency signal input terminal 2 a, LNA group 23 is connected.LNA group 23 includes LNA23 a, LNA23 b and LNA23 c which operate indifferent frequency bands, and are input to MIX circuits 20 a, 20 b and20 c, which operate in different frequency bands, for similarlysignal-processing the output signals from these plurality of LNAs.

LNA23 a, LNA23 b and LNA23 c are provided with switching functions forturning ON and OFF the operating power supplies, respectively (notshown). LNA whose power supply is turned ON amplifies the input signalssupplied from high frequency signal input terminal 2 a and outputs theamplified signals to MIX circuits 20 a, 20 b and 20 c, respectively.High frequency output selecting means 22 selects the high frequencyoutput signals output from MIX circuit 20 a, 20 b and 20 c and outputsone of the selected high frequency output signals to high frequencysignal output terminal 2 b.

Note here that a band for processing signals by the individual LNAs is apart obtained by dividing a wide band of frequency range, and thereby itis possible to obtain excellent communication characteristics with lowpower consumption without increasing the current consumption, which is aproblem in widening the bond of LNA.

Eighth Exemplary Embodiment

FIG. 13 is a block diagram showing an example of a further configurationof a VCO device. The same or corresponding elements shown in the seventhexemplary embodiment shown in FIG. 12 are denoted with the samereference numerals as those therein, and the detailed descriptionthereof is omitted herein.

This is different from FIG. 12 in that BPF (band pass filter) circuit 24provided with a tuning function capable of selecting a frequency isconnected to the output side of LNA group 23. As shown in FIG. 12, LNAgroup 23 includes three LNAs, i.e., LNA23 a, LNA23 b and LNA23 c. Outputsignals from BPF circuit 24 are supplied to MIX circuits 20 a, 20 b and20 c.

When undesired interfering waves are included in a high frequency signalinput to high frequency signal input terminal 2 a, in particular, whenelectric field strength of the interfering waves is strong, byattenuating these interfering waves by the use of BPF circuit 24,excellent communication characteristics can be obtained.

Note here that in FIG. 13, BPF circuit 24 is disposed at the latter partof LNA group 23 but may be disposed at the former part of LNA group 23,that is, at the latter part of high frequency signal input terminal 2 a.Furthermore, it may be disposed both at the former and latter parts ofLNA group 23.

Ninth Exemplary Embodiment

FIG. 14 is a block diagram showing an example of a configuration of areceiver including a VCO device. Note here that the same orcorresponding elements shown in the second exemplary embodiment shown inFIG. 3 are denoted with the same reference numerals as those therein,and the detailed description thereof is omitted herein.

The VCO device shown in FIG. 14 includes received characteristicsjudging means 15. Received characteristics judging means 15 includesdigital demodulation processing circuit 11 and BER judging circuit 12.

The VCO device shown in FIG. 14 has substantially the same currentcontrol means 13 as that shown in FIG. 4. Digital demodulation circuit11 carries out a digital demodulation processing of output signalssupplied from high frequency signal output terminal 2 b and detects BitError Rate (hereinafter, which refers to as “BER”). BER judging circuit12 outputs a digital signal corresponding to the BER detection results.Note here that “BER” represents the quality of the received digitalmodulation signals and is a rate of bit errors included in the bitstring received for a predetermined time.

Current control means 13 outputs an analog signal corresponding to adigital signal output from BER judging circuit 12 and adjusts thecurrent of variable current source circuits 8 a, 9 b and 9 c installedin current source circuit 9.

Then, as an example, as to how the current of variable current sourcecircuit 9 c of VCO circuit 4 c shown in FIG. 14 is adjusted by digitaldemodulation processing circuit 11, BER judging circuit 12 and currentcontrol means 13 is described with reference to FIGS. 15 and 16.

FIG. 15 shows a relation between phase noise (c, d and e) of outputsignal FVCO and current (D, D and E) set by current source circuit 9 cof VCO circuit 4 c shown in FIG. 14 wherein axis of ordinate shows phasenoise and axis of abscissa shows current. In FIG. 15, the relationbetween the above-mentioned phase noise and the above-mentioned currentis shown by a cone-shaped characteristics curve with the minimum phasenoise at current C. When the current is set to values shown by D and Esmaller than C and set to values shown by F and G larger than C, thephase noise becomes larger in both directions.

Therefore, in general, it is preferable that the current is set to C forachieving an excellent receiving performance with a phase noise reduced.However, the relation between the phase noise and current is preferablyreadjusted based on so-called operation environment conditions such assurrounding temperature and power supply voltage. That is to say, it isnoted that when the operation environment is changed, an optimum currentfor minimizing a phase noise is not current C. Therefore, in order tomaintain the excellent receiving performance, the current of currentsource 9 c is adjusted to be optimum corresponding to the change of thereceiving performance so that the phase noise is minimized.

Then, a flowchart shown in FIG. 16 is described with reference to FIGS.14 and 15. FIG. 16 is a flowchart showing a procedure for adjustingcurrent. Note here that in a first step of the flowchart, that is, as aninitial condition, variable current source circuit 9 c of VCO circuit 4c shown in FIG. 15 is set to current C in which the phase noise becomesminimum (S100).

Then, digital demodulation processing circuit 11 carries out digitaldemodulation processing of signals output from high frequency signaloutput terminal 2 b of a receiver including a VCO device so as to detectBER-1 (S102) and, a predetermined time later, detect BER-2 (S104).

As also described before, since “BER” represents a rate of bit errorsincluded in the bit string received for a predetermined time, apredetermined time before and after, BERs are detected and compared witheach other.

Judging circuit 12 compares BER-1 with BER-2, and judges that thereceived result is deteriorated when BER-2 is larger than BER-1 (S106).At this time, current control means 13 sets the current of variablecurrent source circuit 9 c to E that is lower than C for adjusting therelation between the phase noise and current (S108).

Then, similarly, a predetermined time after BER-2 is detected, BER-3 isdetected (S110). When BER-3 is smaller than BER-2, it is judged thatreceived result is improved (S112). At this time, the current ofvariable current source circuit 9 c is set to D that is further lowerthan E. Similarly, after a predetermined time passed, BER-5 is detected(S116). When BER-5 is smaller than BER-3, it is judged that receivedresult is improved. Operation is continued in a state in which thecurrent is set to D (S114). When BER-5 is larger than BER-3, it isjudged that the received result is further deteriorated. The current isreturned to the state of E (S108).

Furthermore, when it is detected that BER-3 is larger than BER-2, it isjudged that the received result is deteriorated. The current of variablecurrent source circuit 9 c is set to F from E (S118). Thereafter, BER-4is detected (S120) and BER-3 and BER-4 are compared with each other(S130). When BER-4 is smaller than BER-3, it is judged that the receivedresult is further deteriorated. The current is set to G that is furtherlarger than F (S124). Then, BER-6 is detected (S126) and BER-4 and BER-6are compared with each other (S128). When BER-6 is smaller than BER-4,it is judged that received result is improved. The operation iscontinued in a state in which the current is set to G (S124). When BER-6is larger than BER-4, it is judged that received result is deteriorated.The operation is continued in a state in which the current is set to G(S118).

Hereinafter, similarly, while the detection and judgment of BER arecarried out, the current of current source circuit 9 is adjustedcorresponding to the change of the received result, whereby the phasenoise characteristics of the VCO device are controlled.

As mentioned above, by adjusting the current of individual VCO circuitscorresponding to the change in BER that represents the superiority orinferiority of characteristics of the receiver, it is possible toachieve a VCO device having excellent phase noise characteristics over awide band by correcting the phase noise even if the operationenvironment such as a temperature and power voltage is changed.

Tenth Exemplary Embodiment

FIG. 17 is a block diagram showing an example of a configuration of areceiver including a VCO device. Note here that the same orcorresponding elements shown in the second exemplary embodiment shown inFIG. 3 are denoted with the same reference numerals as those therein,and the detailed description thereof is omitted herein.

Furthermore, the tenth exemplary embodiment described with reference toFIG. 17 is different from the foregoing other exemplary embodiments inthat digital modulation system judging means 18 is included. Digitalmodulation system judging means 18 includes digital modulation systemdetection circuit 16 and digital modulation system judging circuit 17.Digital modulation system detection circuit 16 detects a digitalmodulation system of an output signal output from high frequency signaloutput terminal 2 b and carries out a digital demodulation processing.

Digital modulation system judging circuit 17 outputs an analog signalcorresponding to a digital modulation system detected by digitalmodulation system detection circuit 16. FIG. 17 further includes currentcontrol means 13. Current control means 13 adjusts the current ofvariable current source circuits 8 a, 9 b and 9 c provided in currentsource circuit 9 corresponding to the analog signal from digitalmodulation system judging circuit 17.

Then, an operation of adjusting the current of VCO circuit 4 c byvariable current source circuit 9 c by way of digital modulation systemdetection circuit 16, digital modulation system judging circuit 17 andcurrent control means 13 is described with reference to FIG. 15, FIG. 18and FIG. 19.

FIG. 18 shows digital modulation systems (required CNR of a receiver)and the corresponding relation between required phase noise and currentof a VCO circuit. Herein, it is assumed that digital modulation system(1), digital modulation system (2) and digital modulation system (3) arerespectively different modulation multiplicities of 256 QAM, 16 QAM andQPSK.

In a general digital modulation system, a system such as 256 QAM havinga high resolution and multiplexed modulation can improve thetransmission speed per unit frequency band. However, it is necessary tosecure a large signal-to-noise power ratio (CNR) of IF signal input froma transmission signal path through a high frequency signal processingsection into a digital demodulation processing means.

In accordance with the digital modulation system of the received signal,a required CNR of a receiver and a required phase noise of a VCO devicemounted on the receiver are determined. In recent radio communication,broadcast communication standards, in which transmission speeds andtransmission quality are diversified by switching the modulation systemsin accordance with the application or using environment, are present.Therefore, it is thought to be a suitable design to maintain ademodulation rate of digital demodulation processing with requiredcharacteristics suitable for respective modulation systems withoutspecifying the noise phase of the VCO device mounted on the receiver toa predetermined value.

Then, as shown in FIG. 18, phase noise c, phase noise e and phase noised respectively corresponding to modulation system (1), modulation system(2) and modulation system (3) are set and current of the VCO circuit isadjusted to C, E and D, whereby the effect of reducing currentconsumption can be obtained when a signal of digital modulation systemwith relatively small modulation multiplicity is received.

FIG. 19 is a flowchart showing an example of an operation for adjustingthe above-mentioned current by a digital modulation system. First ofall, variable current source circuit 9 c of VCO circuit 4 c is set tocurrent C for achieving the largest, i.e., strictest required CNR andfor achieving smaller phase noise c in the plurality of digitalmodulation systems (S200).

Then, digital demodulation processing circuit 11 detects digitalmodulation system (S202). When the detection result is modulation system(2) (S204), the current of variable current source circuit 9 c isreduced to current E (S206) and phase noise e capable of maintaining thedemodulation efficiency of modulation system (2) is realized.

When the modulation system is not modulation system (2), it is judgedwhether or not the modulation system is modulation system (3) (S208).When it is judged that the modulation system is modulation system (3),the current is set to further smaller current D (S210). When themodulation system is not modulation system (3), the current is set tocurrent C again (S200).

Thereafter, similarly, a digital modulation system is detected. When thedigital modulation system is a different modulation system, for example,modulation system (3) continues an operation in a state in which thecurrent is set to the current of variable current source circuitsuitable for the modulation system.

As mentioned above, the VCO device of the present invention can variablyadjust the current of the individual VCO circuits corresponding to thereceived digital modulation systems when high frequency signals, usingsome different digital modulation signals, of broadcast standard orcommunication standard are received or transmitted.

For example, in the digital modulations, when the high frequency signalof a system such as 16 QAM, in which the references are relativelyadjacent to each other and influence of signal deterioration due to asignal-to-noise power ratio (CNR) is large, is processed, the current ofthe VCO circuit is adjusted to increase. On the other hand, when thehigh frequency signal of a system such as QPSK, in which the referencesare not relatively adjacent to each other and the influence of signaldeterioration due to a signal-to-noise power ratio (CNR) is small, isprocessed, the current of the VCO circuit is adjusted to positivelyreduce. Consequently, an effect of realizing a VCO device with a wideband and low current consumption can be obtained.

Note here that in the configuration of the exemplary embodiments of thepresent invention, three VCO circuits are provided. However, the presentinvention is not limited to this, and can be applied to a configurationof a VCO circuit device provided with two or more VCO circuits.

Furthermore, in the exemplary embodiments of the present invention, as asignal selecting means for switching a plurality of VCO circuits, onlyan example of using a switch circuit has been described. However, aconfiguration in which a plurality of configured VCO circuits areelectrically isolated from each other can be used. In addition, aconfiguration in which a signal amplifying means is inserted between theVCO circuit and MIX can be used.

Furthermore, in the exemplary embodiments of the present invention, anexample in which a configuration of high frequency signal processingmeans uses a single conversion system has been described. However, theVCO device of the present invention can be used for a configuration of areceiver including an orthogonal MIX by employing a double-conversionsystem or a direct-conversion system or an IQ output system.

Furthermore, in the exemplary embodiments of the present invention, as acurrent control means for switching currents of a variable currentsource circuit, a configuration of using a current control means hasbeen described. However, it is also possible to use a regulator circuitprovided with a current switching means or a current adjusting means forswitching fixed current. sources by disposing a plurality of fixedcurrent sources with different currents can be used. Furthermore, in aplurality of VCO circuits, current source circuits of a plurality of theVCO circuits other than the VCO circuit necessary for tuning may beturned OFF so that current does not flow therein.

Furthermore, in the exemplary embodiments of the present invention, onlyan example in which a VCO device is used for a receiver has beendescribed. However, the VCO device of the present invention having aneffect of realizing both a wide band of oscillation frequency range andlow current consumption can be widely used for a communication systemincluding a receiver and a transmitter. Furthermore, in mobile equipmentsuch as a movable telephone capable of corresponding to a plurality ofcommunication standards having different frequency bands and inparticular using a battery as a power supply source, an effect of beingable to continuously use transmitting/receiving of video data or audiodata for a long time can be obtained. Furthermore, in the future, whensmall and light tuner is developed and the tuner is installed in mobileequipment such as a mobile telephone etc. using a battery as an electricpower supply source, an effect of being able to continuously reproducevideo data or audio data for a long time can be expected.

Furthermore, in the exemplary embodiments of the present invention, as ajudging means for adjusting the current of the variable current sourcecircuit, only a configuration using a judging index such as BER or adigital modulation system has been described. However, any other judgingindexes can be used.

INDUSTRIAL APPLICABILITY

As mentioned above, since the present invention can provide a VCO devicecapable of achieving both a wide band of an oscillation frequency rangeand low power consumption, the industrial application value thereof ishigh.

1. A VCO device comprising: a plurality of VCO circuits for oscillatingsignals of frequencies corresponding to a control voltage applied to afrequency control voltage terminal, in different oscillation frequencyranges; a current source circuit for respectively setting a drivingcurrent of each of oscillation transistors included in the plurality ofVCO circuits; a signal selecting means for switching output signals ofthe VCO circuits; a PLL for frequency-dividing a local signal selectedby the signal selecting means, comparing a phase thereof with a phase ofa reference signal and outputting a signal converted from a phasedifference; and a loop filter for smoothing the output signal from thePLL and outputting the control voltage for controlling the oscillationfrequency.
 2. The VCO device according to claim 1, wherein in order toequalize phase noises of the plurality of VCO circuits, based on a phasenoise of an oscillation signal of a VCO circuit oscillating in a highestoscillation frequency range in the VCO circuits, current values ofcurrent source circuits of other VCO circuits are set.
 3. The VCO deviceaccording to claim 1, wherein the current source circuit is a variablecurrent source circuit.
 4. The VCO device according to any one of claims1 to 3, comprising a current control means for switching current of thevariable current source circuit corresponding to the oscillationfrequency output from the VCO circuit.
 5. The VCO device according toany one of claims 1 to 4, wherein oscillation frequencies, which areoutput from the plurality of VCO circuits respectively, partiallyoverlap with each other and can be varied continuously into a requiredoscillation frequency range.
 6. The VCO device according to any one ofclaims 1 to 5, wherein each of the plurality of VCO circuits hassubstantially equal oscillation sensitivities by a change in the controlvoltage applied to the frequency control voltage terminal and a changein oscillation frequency corresponding to this control voltage.
 7. TheVCO device according to any one of claims 1 to 6, comprising: aplurality of VCO circuits for oscillating signals. at differentfrequencies corresponding to a control voltage applied to a frequencycontrol voltage terminal; a variable current source circuit forrespectively setting a driving current of each of the plurality of VCOcircuits; a high frequency signal processing means comprising a MIXcircuit connected to output signals from the plurality of VCO circuitsand a high frequency input signal selecting means; a signal selectingmeans for switching the output signals of the VCO circuits; a PLL forfrequency-dividing a local signal selected by the signal selectingmeans, comparing a phase thereof with a phase of a reference signal andoutputting a voltage signal converted from a phase difference; and aloop filter for smoothing the output signal from the PLL and outputtingthe control voltage for controlling the oscillation frequency.
 8. TheVCO device according to claim 7, wherein the high frequency input signalselecting means comprises a low noise amplifier, and further the lownoise amplifier has a power supply ON/OFF function.
 9. The VCO deviceaccording to claim 8, wherein the high frequency input signal selectingmeans comprises a low noise amplifier and has a BPF circuit disposed ata former part or a latter part or both at the former part and the latterpart of the low noise amplifier; the low noise amplifier has a powersupply ON/OFF function; and further the BPF circuit has a tuningfunction capable of selecting frequencies.
 10. The VCO device accordingto any one of claims 3 to 9, comprising: a plurality of VCO circuits foroscillating signals of frequencies corresponding to a control voltageapplied to a frequency control voltage terminal, in differentoscillation frequency ranges; a variable current source circuit forrespectively setting a driving current of each of the plurality of VCOcircuits; a high frequency signal processing means for mixing a localsignal output from any one of the plurality of VCO circuits and areceived signal input from a high frequency signal input terminal; areceived characteristics judging means for carrying out a digitaldemodulation processing of an analog signal output from the highfrequency signal processing means so as to judge receivedcharacteristics; and a current control means for switching currents ofthe variable current source circuit by outputting voltage or currentcorresponding to the digital signal output from the receivedcharacteristics judging means.